Disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and embedded servo sectors. The embedded servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo controller to control the actuator arm as it seeks from track to track.
The head is typically fabricated on a slider which is coupled to the actuator arm through a suspension that biases the slider toward the disk surface. The slider comprises an air-bearing surface (ABS) wherein as the disk rotates, an air-bearing is formed between the slider and the disk that counteracts the bias force of the suspension. Accordingly, the head essentially flies just above the disk surface during write/read operations. Data is typically written to the disk by modulating a write current in an inductive coil of the head to record magnetic transitions onto the disk surface in a process referred to as saturation recording. During readback, the magnetic transitions are sensed by a read element (e.g., a magnetoresistive element) of the head and the resulting read signal demodulated by a suitable read channel. Heat assisted magnetic recording (HAMR) is a recent development that improves the quality of written data by heating the disk surface with a laser during write operations in order to decrease the coercivity of the magnetic medium, thereby enabling the magnetic field generated by the write coil to more readily magnetize the disk surface.
Since the quality of the write/read signal depends on the fly height of the head, conventional heads may comprise an actuator for controlling the fly height. Any suitable dynamic fly height (DFH) actuator may be employed, such as a heater which controls fly height through thermal expansion, or a piezoelectric (PZT) actuator. It is desirable to determine the appropriate DFH setting (e.g., appropriate current applied to a heater) that achieves the target fly height for the head.